Textile materials comprising polyester fibers as a principal component are widely used due to their excellent physical and chemical properties. However, polyester fibers are disadvantageous in that when dyed, they exhibit an inferior brilliance and/or color depth compared with dyed natural keratin fibers, for example, wool and silk; dyed cellulosic fibers, for example, cotton and rayon; and acrylic fibers. This is especially disadvantageous for formal apparel. When polyester fiber materials are dyed a deep color, for example, deep black, the depth of the color is unsatisfactory.
Various attempts have been made to eliminate the above-mentioned disadvantage of dyed polyester fiber materials, for example, improvement of dyes to be applied thereto and chemical modification of the polyester to be converted to the fiber material. However, all these the attempts have produced unsatisfactory results.
One attempt tried to improve the dyeing property of the polyester fiber fabric by applying plasma onto the surface of the polyester fiber fabric at 80 to 500 mA.sec/cm.sup.2 so as to finely roughen the surfaces of the polyester fibers in the fabric. In this case, however, only those surfaces of the polyester fibers to which the plasma was applied could be roughened. The other surfaces of the polyester fibers were quite free from the plasma and not roughened. The partially roughened polyester fibers would later rotate around their longitudinal axes, exposing the non-roughened portions and resulting in uneven color depth and/or brilliance of the resultant fabric.
Another attempt tried to improve the dyeing property of the polyester fibers by roughening their surfaces, by incorporating polyoxyethylene glycol or a mixture of polyoxyethylene glycol with sulfonic acid compound into the bodies of the polyester fibers, and then, by treating the incorporated polyester fibers with an aqueous alkali solution. This method is effective for forming a number of fine pores longitudinally extending along the fibers and on the surface of the fibers. The fine pores cause the resultant porous fiber to be hygroscopic.
Still another attempt tried to produce a surface-roughened polyester fiber by preparing a polyester fiber in which fine particles of an inert inorganic substance, for example, zinc oxide or calcium phosphate are distributed, and then by treating the polyester fiber with an aqueous alkali solution so as to form a number of fine pores in the surface layer of the fiber. This type of fiber was also hygroscopic.
Even the two above-mentioned attempts, however, were not effective for enhancing the depth of color of the dyed polyester fiber. Conversely, they sometimes tended to decrease the depth of the color sensed by the naked eye on the dyed polyester fiber.
That is, in the above-mentioned two attempts, if the polyester fibers were insufficiently treated with the aqueous alkali solution, there was no improvement in the color depth of the dyed polyester fiber. Even if the polyester fibers were sufficiently treated with the aqueous alkali solution and so fine pores were formed on the surface layer of the fiber to the desired extent, the pores resulted in diffused reflection of light on the surface of the dyed fiber. This resulted in the reduction in the depth of color sensed by the naked eye of the dyed fiber and caused a pale hue of the dyed fibers. Also, the alkali treatment sometimes causes a significantly decreased mechanical-strength of the polyester fibers and/or an increased the fibril-forming property of the polyester fibers to such an extent that the resultant alkalitreated polyester fibers could not be used in practice.
In a further attempt, polyester fibers containing fine inorganic particles having a size of 80 microns or less, for example, silica particles, and evenly dispersed therein were prepared. They were then treated with an aqueous alkali solution so as to roughen the surface of the fibers to a roughness in the range of from 50 to 200 microns. After dyeing, however, the color depth of the resultant polyester fibers turned out to be similar to that of polyester fibers treated with the aqueous alkali solution but not containing inorganic particles. Even when the surface-roughened polyester fibers were further treated with the aqueous alkali solution, this merely resulted in further reduction of the thickness of the fibers and in further roughening of the surface of the fibers without improving the color depth of the dyed fibers.
Also, in the above-mentioned attempts, it was found that application of a mechanical force, for example, rubbing force, to the roughened surface of the dyed polyester fiber would smooth out the roughened surface, resulting in a different color and glass between the smoothed portion of the fiber surface and the non-smoothed portion of the fiber surface.
Furthermore, the fibril-forming property of the polyester fiber is undesirably enhanced by the presence of the inorganic particles in the fiber.